How do I connect my Win7 and XP Home PC's to share my broadband cable modem

A while back the hard drive of my 8yr old Win XP Home PC went kaput. I then built myself a new Win7 64bit PC which I have used without problem since last xmas. Having got a rebate from Ebuyer for some faulty memory I decided to buy a replacement hard drive for my old XP PC with the intention of keeping it as a backup.

I installed the new hard drive and Win XP Home SP2 installed without a hitch. Now I would like to go online with my old XP PC in order to update it to the latest SP3 updates and register it for verification. I googled this and as it is not my intention to create a network with two PC's I would like to know what is the easiest way to connect it to the internet in order to achieve this. I googled some solutions and for my purpose it appears that I need to buy a crossover cable to connect PC1 Win7 to PC2 XP Home. However when I look at the back of my PC's they each have only one RJ45 connection socket, so I am confused as how I do this as according to the diagram the crossover cable goes from the RJ45 socket in the Win7 PC to the RJ45 socket in the XP Home PC but as there are only one RJ45 socket on each PC there is nowhere to plug in the cable modem lead. Does anyone have any idea of how I can accomplish this?. Thanks in advance for any help offered.

Easiest solution I know is to install a desktop network switch which you install between the modem and your computers and it provides internet connection for both.

Cheap ones are available on eBay for about $9, plus you will need two network cables for about $3 each on eBay. You simply plug in the switch and turn it on. Remove the plug from your computer and put it in the input of the switch. Then plug the two new cables into Port1 and Port2 of the switch and the other ends into the computers.